A transverse fracture through the middle third and proximal third of the patella, are classified by AO/OTA as a 34C1.1 and 24C1.2 fracture respectively.
These fractures are characterized by a complete disruption of the extensor apparatus of the knee. They may be due to a hyperflexion injury, with a sudden quadriceps contraction when the knee is flexed. This is typical in the middle-aged adult as a mechanism. The patellofemoral joint surface may be injured, associated with impaction deformation of the patellar joint surface that can be difficult to restore anatomically and stably. If the fragments are separated the extensor mechanism is usually disrupted.
When the fracture occurs through the proximal third of the patella, it is classified by AO/OTA as a 34C1.2 fracture.